In LTE (Long Term Evolution)-Advanced, a PDCP (Packet Data Convergence Protocol) layer is provided in mobile stations UE and radio base stations eNB.
The PDCP layer on a transmitting side is configured to perform ciphering processing and tampering detection processing on PDCP-SDUs (Service Data Units) received from a RRC (Radio Resource Control) layer by using COUNT values, and to transmit PDCP-PDUs (Protocol Data Units) given PDCP-SNs (Sequence Numbers) as headers to a RLC (Radio Link Control) layer.
In this respect, as illustrated in FIG. 5, the COUNT value is composed by an HFN (Hyper Frame Number) and a PDCP-SN.
Here, the PDCP-SN has 12 bits (or 7 bits), and is configured to be incremented every time a PDCP-PDU is generated and transmitted to the RLC layer. Meanwhile, the HFN has 20 bits (or 25 bits) and is configured to be incremented every time a cycle of the PDCP-SNs completes.
On the other hand, the PDCP layer on the receiving side is configured to perform the deciphering processing and tampering detection processing by using the COUNT values.
Specifically, as illustrated in FIG. 6, the PDCP layer on the receiving side is configured to discard a received PDCP-PDU if the PDCP-SN given as the header to the PDCP-PDU is out of a receive window.
On the other hand, the PDCP layer on the receiving side is configured to, if the PDCP-SN given as the header to a received PDCP-PDU is within the receive window, perform the deciphering processing and tampering detection processing on the PDCP-PDU by using the aforementioned COUNT value and update the receive window.
Moreover, if a handover procedure or a reconnection procedure is activated as illustrated in FIG. 7, the PDCP layer on the transmitting side is configured to retransmit PDCP-PDUs (FIG. 8, PDCP-PDUs #2-#8) to the mobile station UE after completion of the handover procedure or the reconnection procedure as illustrated in FIG. 8. Note that the PDCP-PDUs retransmitted herein are PDCP-PDUs multiplexed on an RLC-PDU for which the successful delivery has not been confirmed in the RLC layer, and all the following PDCP-PDUs.
On the other hand, the PDCP layer on the receiving side is configured to update the receive window according to a result of the receipt of the RLC-PDU on which the PDCP-PDUs are multiplexed, as illustrated in FIGS. 7 and 8.